In many systems for wireless communications, a network node is communicating with one or more terminal nodes or terminals. The network nodes may be referred to as evolved Node B (eNB), base station (BS), Access Point (AP), etc. depending on which communication standard being discussed. Analogously, the terminal node may also be referred to as user equipment (UE), station (STA), etc. In the following the terms network node and terminal will be used as generic terms for such communicating entities.
In many situations, the network node is connected to the main power supply, whereas the terminal is battery powered. This means that power consumption typically is more of an issue for the terminal than it is for the network node. Another differentiating characteristic between a network node and a terminal is that it is typically possible to justify a considerably higher cost for the network node, allowing the use of components that support higher output power for a radio transmitter in the network node.
In summary, it is quite a common scenario that the network nodes have considerably higher output power than the output power of a terminal. Therefore, the downlink (DL), i.e. the radio link in the direction from the network node to the terminal, is often more reliable than the uplink (UL), i.e. the radio link in the direction from the terminal to the network node. This difference in reliability between the UL and DL has a consequence that, even if the DL provides a geographical coverage that is of a certain size, the lesser reliability of the UL has the consequence that a terminal may not be able to communicate when located far from the network node but still within the geographical coverage area of the DL. In other words, there is typically an asymmetry or imbalance between the coverage areas of the UL and the DL.
This asymmetry means that higher data rate can be supported in the DL than in the UL. However, what is even more of an issue is that often DL data needs to be acknowledged, i.e. an ACK message being transmitted in the UL that indicates to the network node that the data packet (data message) transmitted in the DL was correctly received by the terminal.
Typically, according to existing solutions, the above mentioned asymmetry in the capability of supporting high data rates in the DL and the UL is counteracted by using more robust modulation and coding scheme in the UL. However when the asymmetry is too large, the UL will still severely limit the coverage also for the DL.
US 2013/0235746 A1 describes a method in a node for selecting channels of different frequency bands in so-called femtocells. Criteria such as the location of the node in relation to a building are used in the selection of frequency bands.